1. Field of the Invention
The present invention relates generally to line pressure control arrangements for automatic automotive transmissions and more specifically to a line pressure control arrangement which is responsive to the operation of a traction control which modifies the amount of torque produced by an engine associated with an automatic transmission.
1. Description of the Prior Art
JP-A-62-31769 discloses a traction control arrangement wherein the output of the engine is varied in accordance with the amount of wheel slip. In this arrangement, first and second throttles are arranged in series in the induction conduit. This so-called tandem throttle valve arrangement is such that one of the throttle valves is controlled in accordance with the amount of accelerator pedal depression while the other is controlled by a traction control system.
JP-A-62-62047 discloses a transmission control arrangement wherein the level of line pressure which is used to engage and disengage the various friction elements of the transmission is varied in accordance with the load on the engine as indicated by the position of the throttle valve, in order to attenuate shift shock.
However, in the event that a shift shock attenuation arrangement of the nature disclosed in JP-A-62-62047 is applied to a transmission which is operatively connected to an engine equipped with a tandem throttle valve type traction control arrangement, a problem may be encountered in that the level of line pressure is controlled only in accordance with the position of the accelerator pedal operated throttle valve. That is to say, in the event that the traction control is active and closes the second throttle valve more than the first accelerator pedal operated one, the amount of torque produced by the engine is lower than that indicated by the position of the first throttle valve and the level of the line pressure is controlled to a level which is higher than suited for the amount of torque actually being produced by the engine. This results in the engagement of the transmission friction elements being controlled in a manner which invites the generation of shift and selection shocks.